Polyurea/urethane membranes and their use for the separation of aromatics from non-aromatics are the subject of U.S. Pat. No. 4,914,064. In that case the polyurea/urethane membrane is made from a polyurea/urethane polymer characterized by possessing a urea index of at least about 20% but less than 100%, an aromatic carbon content of at least about 15 mole percent, a functional group density of at least about 10 per 1000 grams of polymer, and a C.dbd.O/NH ratio of less than about 8.0. The polyurea/urethane multi-block copolymer is produced by reacting dihydroxy or polyhydroxy compounds, such as polyethers or polyesters having molecular weights in the range of about 500 to 5,000 with aliphatic, alkylaromatic or aromatic diisocyanates to produce a prepolymer which is then chain extended using diamines, polyamines or amino alcohols. The membranes are used to separate aromatics from non-aromatics under perstraction or pervaporation conditions.
The use of polyurethane imide membranes for aromatics from non-aromatics separations is disclosed in U.S. Pat. No. 4,929,358. The polyurethane-imide membrane is made from a polyurethane-imide copolymer produced by end capping a polyol such as a dihydroxy or polyhydroxy compound (e.g. polyether or polyester) with a di or polyisocyanate to produce a prepolymer which is then chain extended by reaction of said prepolymer with a di or polyanhydride or with a di or polycarboxylic acid to produce a polyurethane/imide. The aromatic/non-aromatic separation using said membrane is preferably conducted under perstraction or pervaporation conditions.
A polyester imide copolymer membrane and its use for the separation of aromatics from non-aromatics is the subject of U.S. Pat. No. 4,946,594. In that case the polyester imide is prepared by reacting polyester diol or polyol with a dianhydride to produce a prepolymer which is then chain extended preferably with a diisocyanate to produce the polyester imide.
The use of membranes to separate aromatics from saturates has long been pursued by the scientific and industrial community and is the subject of numerous patents.
U.S. Pat. No. 3,370,102 describes a general process for separating a feed into a permeate stream and a retentate stream and utilizes a sweep liquid to remove the permeate from the face of the membrane to thereby maintain the concentration gradient driving force. The process can be used to separate a wide variety of mixtures including various petroleum fractions, naphthas, oils, hydrocarbon mixtures. Expressly recited is the separation of aromatics from kerosene.
U.S. Pat. No. 2,958,656 teaches the separation of hydrocarbons by type, i.e. aromatic, unsaturated, saturated, by permeating a portion of the mixture through a non-porous cellulose ether membrane and removing permeate from the permeate side of the membrane using a sweep gas or liquid. Feeds include hydrocarbon mixtures, naphtha (including virgin naphtha, naphtha from thermal or catalytic cracking, etc.).
U.S. Pat. No. 2,930,754 teaches a method for separating hydrocarbons e.g. aromatic and/or olefins from gasoline boiling range mixtures, by the selective permeation of the aromatic through certain cellulose ester non-porous membranes. The permeated hydrocarbons are continuously removed from the permeate zone using a sweep gas or liquid.
U.S. Pat. No. 4,115,465 teaches the use of polyurethane membranes to selectively separate aromatics from saturates via pervaporation.
U.S. Pat. No. 4,929,357 is directed to non-porous isocyanurate crosslinked polyurethane membranes. The membrane can be in the form of a symmetric dense film membrane. Alternatively, a thin, dense layer of isocyanurate crosslinked polyurethane can be deposited on a porous backing layer to produce a thin film composite membrane. The isocyanurate crosslinked polyurethane membrane can be used to separate aromatic hydrocarbons from feed streams containing mixtures of aromatic hydrocarbons and non-aromatic hydrocarbons, the separation process being conducted under reverse osmosis, dialysis, perstraction or pervaporation conditions, preferably under perstraction or pervaporation conditions.
U.S. Pat. No. 4,366,062 teaches reverse osmosis using a composite isocyanurate membrane. The method selectively separates at least one water soluble material from an aqueous solution. The membrane comprises a microporous substrate and a barrier layer about 0.01 to 0.1 micron thick. It is composed of a crosslinked polymeric material having isocyanurate structure and substituents appended thereto selected from hydrogen, glycidyl groups and alkyl radical groups containing 2 to 5 carbon atoms which may also contain functional hydroxyl groups or glycidyl groups. The crosslinked polymeric material has ester or ether linkages or combination thereof connecting the isocyanurate structures to each other.
U.S. Pat. No. 4,557,949 teaches a method for making the reverse osmosis semipermeable membrane disclosed in U.S. Pat. No. 4,366,062.
European Application 0044872 teaches selectively separating water soluble materials from a solution under reverse osmosis conditions using a membrane having a porous support layer carrying a barrier layer of crosslinked isocyanurate polymer.
Japanese Application 81/160960 teaches a composite membrane for reverse osmosis made by applying a solution of a barrier layer-forming component to a substrate, then heating it.
Japanese Application 78/121150 teaches an isocyanurate network terpolymer useful for the production of a selective permeation membrane. A polymer having hydroxyl groups and tert amine groups in the side chain is reacted with cyanuric chloride and subject to terpolymerization by reacting the tert amine groups with produced hydrochloride to give a polymerized polyisocyanurate. A polymer made using glycidyl methacrylate-styrene copolymer, diethyl amine in benzene and methanol was produced having 2-hydroxy-3-diethylaminopropyl group. This polymer was crosslinked with cyanuric chloride and cast on a PTFE plate and kept 24 hours at 40.degree. to give a 44.mu. membrane. This membrane was used to separate a mixture of cyclohexane and benzene under pervaporation conditions. A permeate gas which was 100% benzene was recovered at a rate of 0.0025 g/m.sup.2 -hr.